Adsorption
|
A process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a film of molecules or atoms (the adsorbate). Most industrial adsorbents fall into one of three classes: 1. Oxygen-containing compounds (e.g.silica gel and zeolites 2. Carbon-based compounds (e.g. activated carbon and graphite) 3. Polymer-based compounds
|
By blocking the field as it enters of leaves the surface at which adsorption has taken place
|
Angular Momentum Conservation
|
In a closed system angular momentum is constant. The conservation of angular momentum explains the angular acceleration of an ice skater as she brings her arms and legs close to the vertical axis of rotation. By bringing part of mass of her body closer to the axis she decreases her body's moment of inertia. Because angular momentum is constant the angular velocity (rotational speed) of the skater has to increase.
|
Birefringence
|
Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals or boron nitride, depending on the polarisation of the light. This effect can occur only if the structure of the material is anisotropic (directionally dependent).
|
Dielectric
|
An electrical insulator that can be polarized by an applied electric field.Can be used for the storage and dissipation of electric and magnetic energy.
|
Dielectric Permittivity
|
The measure of how much resistance is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. Thus, permittivity relates to a material's ability to transmit (or 'permit') an electric field.
|
In the case of an electric field.
|
Echo
|
A reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound.
|
Electrical Resistance
|
The degree to which an object opposes an electric current flowing through it (usually measured in Ohms). A function of both its physical geometry and the resistivity of the material the object is made from.
|
Electro-Optic Effects
|
A change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light. The term encompasses a number of distinct phenomena, which can be subdivided into a) change of the absorption (electroabsorption, Franz-Keldysh effect, Quantum-confined Stark effect, electro-chromatic effect) and b) change of the refractive index(Pockels effect, Kerr Effect, electro-gyration)
|
Electrochromism
|
A type of electro-optic effect. The creation of an absorption band at some wavelengths in a material in response to an electric field, which gives rise to a change in colour (i.e. the phenomenon displayed by some chemical species of reversibly changing color when a burst of charge is applied).
|
Fluorescence
|
Fluorescence is a luminescence that is mostly found as an optical phenomenon in cold bodies, in which the molecular absorption of a photon triggers the emission of a photon with a longer (less energetic) wavelength. The energy difference between the absorbed and emitted photons ends up as molecular rotations, vibrations or heat. Sometimes the absorbed photon is in the ultraviolet range, and the emitted light is in the visible range.
|
The frequency of the stimulating radiation is different from that of the emitted radiation.
|
Focusing
|
The gathering of wavefronts of a wave (e.g. radiation) into a spherical or cylindical shape. Focusing of light is used in optics, however focusing can be applied to any radiation or wave.
|
Kerr Effect
|
(or the quadratic electro-optic effect) A change in the refractive index of a material in response to an electric field. Distinct from the Pockels effect in that the induced index change is directly proportional to the square of the electric field instead of to the magnitude of the field. All materials show a Kerr effect, but certain liquids display the effect more strongly than other materials.
|
Liquid Crystals
|
Substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal.
|
Magnetic Field
|
A vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.
|
Magnetic Hysteresis
|
Hysteresis phenomena occur in magnetic and ferromagnetic materials, as well as in the elastic, electric, and magnetic behavior of materials, in which a lag occurs between the application and the removal of a force or field and its subsequent effect. Magnetic field hysteresis loss causes heating. This effect is used in induction cooking, where an alternating magnetic field causes a ferrite container to heat directly rather than being heated by an external heat-source.
|
Magnetic Reluctance
|
Analogous to the way an electric field causes an electric current to follow the path of least resistance, a magnetic field causes magnetic flux to follow the path of least magnetic reluctance.
|
Magnetic Saturation
|
Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetising field cannot increase the magnetisation of the material further, so the total magnetic field levels off. It is a characteristic particularly of ferromagnetic materials, such as iron, nickel, cobalt and their alloys.
|
Magnetism
|
One of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic field.
|
Metastability
|
A general scientific concept which describes states of delicate equilibrium. A system is in a metastable state when it is in equilibrium (not changing with time) but is susceptible to fall into lower-energy states with only slight interaction. It is analogous to being at the bottom of a small valley when there is a deeper valley close by
|
Non-Newtonian Fluids
|
Fluids whose flow properties are not described by a single constant value of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the strain rate is nonlinear, and can even be time-dependent. Therefore a constant coefficient of viscosity can not be defined. A ratio between shear stress and rate of strain (or shear-dependent viscosity) can be defined, this being more useful for fluids without time-dependent behavior.
|
For example, mechanical force, in the case of body armour.
|
Physical Containment
|
Partial or complete enclosure of an object or substance by some physical medium, typically for the purpose of protection or restriction of movement.
|
Pockels Effect
|
Produces birefringence in an optical medium induced by a constant or varying electric field. Used to make Pockels cells, which are voltage-controlled wave plates.
|
Polarisation
|
A property of waves that describes the orientation of their oscillations. For transverse waves such as many electromagnetic waves, it describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel. The oscillations may be oriented in a single direction (linear polarisation), or the oscillation direction may rotate as the wave travels (circular or elliptical polarisation).
|
Purkinje effect
|
The tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.This effect introduces a difference in color contrast under different levels of illumination.
|
Reverberation
|
The persistence of sound in a particular space after the original sound is removed. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air.This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard.
|
Shadow
|
An area where direct light (or other radiation) from a source cannot reach due to obstruction by an object. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light (or radiation).
|
Sorption
|
The action of both absorption and adsorption taking place simultaneously, i.e. the effect of gases or liquids being incorporated into a material of a different state and adhering to the surface of another molecule. Absorption is the incorporation of a substance in one state into another of a different state (e.g., liquids absorbed by solid or gas absorbed by liquid). Adsorption is the physical adherence or bonding of ions and molecules onto the surface of another molecule.
|
By blocking the field as it enters of leaves the surface at which sorption has taken place
|
Stress Relaxation
|
The decrease in stress with time in a viscoelatic material held at constant strain or deformation.
|
Surface Acoustic Wave
|
(SAW) An acoustic wave traveling along the surface of a material having some elasticity, with an amplitude that typically decays exponentially with the depth of the substrate. This kind of wave is commonly used in devices called SAW devices in electronics circuits.
|
Total Internal Reflection
|
An optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.
|
